The disclosed invention relates to the field of coherent light transmission devices, and in particular, to the correction of the beam profiles of the light beam emitted by semi-conductor lasers.
In high speed random access optical recording systems, it is well known to use a modulated and focused radiation beam, usually a laser, to record both digital and analog information on a recording surface. In recent years, there has been increased interest in the development of optical storage devices which can record as well as read optical information. See e.g. U.S. Pat. No. 4,363,116, issued Dec. 7, 1982, to Kleuters et al., wherein a single laser is used to both record data on, and to read data from, the disk surface. In Kleuters, this dual purpose is accomplished by switching the laser from a higher intensity write beam to a lower intensity read beam. There has also been increased interest in the use of multi-laser systems for both reading and writing. See U.S. Pat. No, 4,198,701, issued Apr. 15, 1980, to Reddersen et al., wherein a first beam is used for writing data, and a second beam is used for reading data. See also U.S. Pat. No. 4,334,299, issued June 8, 1982, to Komurasaki et al.
In the early optical recording devices, gas lasers were used to read and write data. However, the power output of semiconductor lasers has increased and sustained performance has become more reliable. See U.S. Pat. No. 4,360,920, issued Nov. 23, 1982 to Woda et al.; and U.S. Pat. No. 4,360,919, issued Nov. 23, 1982, to Fijiwara et al. As a result, diode lasers have begun to be used in optical recording devices to read and, more recently, to write user data. See for example U.S. Pat. No. 4,345,321, issued Aug. 17, 1982 to Arquie et al. However, the performance characteristics of diode lasers still vary widely from individual laser to individual laser. Accordingly, where standardized output for reading or writing is required, it has been necessary to custom design the optics in the device according to the specific output characteristics of the individual laser diode mounted in the device. See U.S. Pat. No. 4,322,838, issued Mar. 30, 1982, to Neumann, disclosing a collimating system; U.S. Pat. No. 4,333,173, issued to Yonezawa et al., and; U.S. Pat. No, 4,128,308, issued Dec. 5, 1978 to McNaney.
Diode lasers emit beams which are uncollimated, have non-circular cross-sections, and have astigmatic focal points. In addition, the power output varies significantly from laser to laser. Therefore, for the laser to be used in most applications and in particular in optical storage and retrieval devices where diffraction limited spot sizes are desired, the output profile of the beam must be standardized. Specifically, the cross-section of the beam must be circularized, the beam must be collimated, and the original astigmatism must be corrected. Complex lens systems have been developed which can separately correct for astigmatism, un-collimation, and a non-circular beam cross-section. To date, these systems have been rather bulky and most difficult to adjust due to the complex number of elements required. What is needed then is a simpler, more efficient, means of circularizing and de-astigmatizing the incident beam. The present invention provides just such a means.
It is an object of this invention to provide a means for efficiently circularizing a diode laser beam having a non-circular cross-section.
It is another object of the disclosed invention to provide a means for efficiently de-astigmatizing the astigmatic laser beam emitted by diode lasers.
It is still another object of the disclosed invention to provide a means for efficiently collimating the divergent laser beam emitted by diode lasers.
It is yet another object of the disclosed invention to provide a means for the in-line circularization of an un-circularized laser beam emitted by diode lasers.
It is still yet another object of the disclosed invention to provide a means for the in-line de-astigmatizatin of an astigmatic laser beam emitted by diode lasers.
It is yet still another object of the disclosed invention to provide a single combined means for the in-line, cross-section correction and de-astigmatization of the incident laser beam emitted by diode lasers.